The present invention relates to a wheel rim in which both ends of an annular rim part (with respect to the direction of width of the rim) are equipped with rim flanges, and a manufacturing method which is used to manufacture this wheel rim.
For example, cast one-piece wheels which are manufactured by causing a molten metal to flow into a mold are available as wheels; however, two-piece wheels (assembled from two parts, i.e., an annular rim part and a disk part) and three-piece wheels (assembled from three parts, i.e., an annular outer rim part, an annular inner rim part and a disk part) which make it possible to enhance the fashion characteristics of the area around the disk surface, and which are advantageous in terms of productivity, have attracted attention in recent years.
Furthermore, in regard to the abovementioned wheels, the following two types of wheels have been proposed in order to make the rim part thinner for the purpose of reducing the weight of the wheel, and also in order to increase the rigidity so that there is no damage such as cracking or the like or deformation of the rim flanges disposed on both ends of the rim part, in which there is a maximum concentration of stress from the tires during operation of the vehicle.
First, the first wheel is a wheel equipped with rim flanges in which both end portions of the rim part are folded double and press-bonded as indicated in Japanese Patent Application Laid-Open No. 2001-259769.
Furthermore, the second wheel is a wheel in which both ends of the rim part are bent and molded to the inside (which is the tire attachment side), and the insides of the bent and molded portions are lined with a wire ring, as indicated in Japanese Utility Model Application Laid-Open No. 62-165102.
Furthermore, the rigidity might conceivably be increased by making the thickness of the rim flanges thicker than the thickness of the rim part by casting or the like; in such a case, however, there are disadvantages in terms of cost. Accordingly, the rigidity of the rim flanges is increased by folding or pressing plate materials of the same thickness.
In the case of the first wheel mentioned above, both end portions of the rim are merely folded double and press-bonded; accordingly, it cannot be guaranteed that the thickness of the rim flanges is twice the thickness of the rim part, and there is a danger of damage such as cracking or deformation of the rim flanges. Furthermore, if a gap is generated between the contact surfaces of the folded portions and non-folded portions in the abovementioned folded and press-bonded state, there is a danger of a drop in strength due to cracking or the like in these portions. Accordingly, it is necessary to press-bond the end portions on the folded side of the rim part to the end portions on the non-folded side by means of a large force; as a result, the end portions of the rim part are crushed in some areas, so that the thickness of the rim flanges is actually less than twice the thickness of the rim part, as was described above, thus making it impossible to eliminate the abovementioned problem. In this case, increasing the thickness of the plate material that forms the rim part might be conceivable. In such a case, however, the overall weight of the wheel is increased; accordingly, such an approach is difficult in practical terms, and there is room for improvement.
Furthermore, in the case of the second wheel, not only are wire rings that constitute separately formed extra parts required, but the bothersome work of attaching these wire rings during the molding of the wheel is necessary. Moreover, because of this lining with wire rings, gaps are generated between the bend molded parts that are molded by bending and the non-bent parts; as a result, although the strength is increased in the areas where the wire rings are located, there is an extreme drop in strength in the areas that lack these wire rings.
With the foregoing in view, it is an object of the present invention to provide a wheel rim which is equipped with rim flanges that show no deformation or damage, even though the weight of the wheel rim is reduced.
In order to achieve the abovementioned object, the present invention constructs a wheel rim which is equipped with a rim flange consisting of a double structure in which at least the outer-side end portion of the opposite ends across the rim part is folded back toward the inside which is the tire attachment side, and caused to contact the non-folded portion of the rim part without any gap, and wherein said folded portion and said non-folded portion respectively have thicknesses that are greater than the thickness of said rim part, and a curved part which is smoothly continuous with the surface of said non-folded portion is provided on the free end portion of said folded portion.
Accordingly, since the rim flange is formed with a double structure consisting of a folded portion and a non-folded portion, and since the respective thicknesses of the folded portion and the non-folded portion are thicker than the thickness of the rim part, the thickness of the rim flange is a thickness that is more than twice the thickness of the rim part, so that an increase in strength compared to conventional wheels can be realized. Furthermore, since the folded portion and the non-folded portion are caused to contact each other in a state in which there is no gap, the desired strength can be obtained in all portions of the rim flange. Moreover, since the outer side end portion is folded to the inside, which is the tire attachment side, the folded free end portion is hidden by the tire, and is therefore not exposed in a position that can be seen from the outside. Accordingly, there is no loss of the design characteristics of the wheel. Furthermore, the free end portion of the folded portion has a curved part that is smoothly continuous with the surface of the non-folded portion; accordingly, even in cases where the free end portion of the folded portion has a corner part that protrudes with respect to the non-folded portion, damage to the tire caused by the contact of this corner part with the tire, and the deposition of foreign matter such as mud, dirt or the like on this corner part, can be securely avoided.
In the present invention, the rim flange of the wheel is formed by curling means for curling at least the outer side end portion of the opposite ends across the, rim toward the inside which is the tire attachment side in a curvilinear manner; and by roll-forming means for forming the free end portion of said folded portion so that this free end portion is smoothly continuous with the surface of said non-folded portion, while simultaneously producing a double structure in which the curled portion that has been curled by said curling means is folded back and laid on the non-curled portion without any gap by pressing same against the non-curled portion, and for performing finish forming so that the thickness of said folded portion that is folded back and the thickness of the non-folded portion that is caused to contact said folded portion in a state in which there is no gap therebetween are specified thicknesses that are greater than the thickness of said rim part.
Since the rim flange is formed with a double structure using curling means and roll-forming means as described above, the rim flange can be molded so that this rim flange has a specified thickness that is more than twice the thickness of the rim part, so that an increase in strength compared to conventional wheels can be reliably accomplished. Furthermore, since the outer side end portion is folded to the inside (which is the tire attachment side) in the same manner as in the first invention, the folded free end portion is hidden by the tire, and is therefore not exposed in a position that can be seen from the outside. Accordingly, there is no loss of the design characteristics of the wheel. Furthermore, the free end portion of the folded portion has a curved part that is smoothly continuous with the surface of the non-folded portion; accordingly, even in cases where the free end portion of the folded portion has a corner part that protrudes with respect to the non-folded portion, damage to the tire caused by the contact of this corner part with the tire, and the deposition of foreign matter such as mud, dirt or the like on this corner part, can be securely avoided.
The above-mentioned curling means are means for curling the outer side end portion so that, when the outer side end portion is curled to the inside, the resulting thickness is greater than said specified thickness, and the above-mentioned d roll-forming means are means which press the free end side of said curled portion against said non-curled portion so that the free end portion of said folded portion is smoothly continuous with the surface of said non-folded portion, while at the same time perform finish forming of said folded portion and non-folded portion into a specified shape so that the thickness of said folded portion and the thickness of the non-folded portion that is caused to contact said folded portion in a state in which there is no gap therebetween are specified thicknesses that are greater than the thickness of said rim part.
When the outer side end portion is curled to the inside by the curling means, the curled part is deformed toward the compression side, so that the thickness is increased by an amount corresponding to this compression. Utilizing this, it is possible to perform curling so that the resulting thickness is greater than the abovementioned specified thickness by a desired amount. Furthermore, it is possible to mold the curled portion that is reached the abovementioned specified thickness to a further specified thickness using the roll-forming means, and to perform finish forming into a specified shape by pressing the free end portion of the curled portion so that this free end portion is smoothly continuous with the surface of the non-folded portion.